Many different methods are known for packaging integrated circuits. In one method, an integrated circuit is die bonded face-side up to a metal leadframe. The leadframe is made of stamped metal and includes a plurality of radially extending leads. The leadframe is one leadframe of many in a strip of leadframes. The leads of each leadframe are held together by rails of metal material. Once the integrated circuit is attached to the center of the leadframe, each individual bond pad on the integrated circuit is typically wire bonded to the tip of an associated one of the radially extending leads. After the wire-bonding process is completed, a plastic encapsulant is injection molded around the die and wire bonds such that the leads extend outward from the plastic. After the plastic has hardened, the rails are typically cut away to singulate the leads from one another and to separate the resulting integrated circuit package from other packages formed onto a strip of such leadframes. The outwardly extending leads are bent into a desired shape for a lead of the resulting package. Performing the wire bonding step in the above-described packaging process involves cost.
In a second method, often referred to as “flip-chip” packaging or Controlled Collapse Chip Connection (C4) packaging, a small bonding bump of conductive material such as solder is formed on each contact pad of the integrated circuit. These flip-chip bonding bumps extend upward from the surface of the face side of the integrated circuit. Rather than wire bonding pads of the integrated circuit to the various leads of the package, the integrated circuit is placed face-side down such that the bond bumps extend down and make electrical and physical contact with tips of the leads. In one example, the leads are leads of stamped metal as described above. A soldering process is then performed such that the integrated flip-chip bond bumps are soldered to the integrated circuit pads to the leads. A plastic encapsulant is then injection molded around the die such that the leads extend outward from the plastic. After the plastic has hardened, the rails are then cut away to singulate the package as in the wire-bonded example explained above and the leads a bent into the desired lead shape.
There are many different variations of flip-chip bonding, and the technique works well, but there are costs to using the technique. Extra semiconductor processing steps are involved in growing and/or placing the flip-chip bond bumps on the die. Under-bump metallization (UBM) layers must generally be provided. The extra steps in fabricating these structures and layers would otherwise not need to be performed if the flip-chip bond bumps were not provided on the integrated circuit. Carrying out the extra bump-forming steps therefore involves an expense. Moreover, there are often licensing payments that must be made and intellectual property issues that must be addressed in order to use many flip-chip packaging processes. Avoiding those costs and complexities is desired.
Bare integrated circuit dice can be directly reflow soldered to printed circuit boards of electronic consumer devices without integrated circuit packages, but this generally involves the semiconductor manufacturer losing control of the dice and can introduce reliability problems. For example, solvents used to clean printed circuit boards in printed circuit board assembly houses, if such solvents come into contact with bare semiconductor dice, can compromise the dice and affect the future reliability of the dice. Bonding bare dice directly to printed circuit boards of ultimate electronic consumer devices is therefore to be avoided. A suitable low-cost integrated circuit package is needed.